Molded parts used for photographic sensitive materials and resin compositions used to make thereof

ABSTRACT

A novel resin composition for use in applications requiring low formaldehyde concentration levels. The novel composition comprising a stabilized polyacetal polymer with capped end groups is characterized by the concentration of formaldehyde generated from a formed object of the said composition in a closed environment being less than 20 ppm.

BACKGROUND OF THE INVENTION

1. Industrial Use Field

This invention pertains to molded parts used for photographic sensitivematerials and resin compositions used to make such parts as magazineswhich house photographic sensitive materials like photo-film andprinting paper or springs and rollers that are used around thephotographic sensitive materials.

2. Existing Technology

Polyacetal resin which is a thermoplastic resin is used as a moldingcomposition for machine bearings, gear wheels, rollers, cams, clips andplate springs because of its excellent mechanical properties, heatresistance, friction resistant and anti-abrasion properties and fatigueresistance property. However, a small amount of the monomer formaldehydeis dissolved in molded parts made of the polyacetal resin and its slowrelease into the air causes deterioration of work environment andcompromized work efficiency and, in some cases, may lead to harmfulresult to the end use objective. For example, because chemically activeformaldehyde is present, the polyacetal resin causes some concern to beused as food and medical packaging material.

Also, it is known that formaldehyde has detrimental effect onphotographic sensitive materials such as photographic film and printingpaper. While a silver halide emulsion is used in these photographicsensitive materials, formaldehyde has the ability to reduce silverhalides, resulting in chemical fogging. Therefore, polyacetal resins, ingeneral, cannot be used as a resin composition of magazines that receivephotographic sensitive materials and various molded parts that are usedaround them. Consequently, metals are often used to make parts thatrequire sufficient elasticity such as a film pressing board.

Considering these situations and in order to reduce concentrations offormaldehyde gas in the molded parts made of acetal resin, JapaneseKokai 1992-34548 describes hydrazide compounds to be used as anadditive, and Japanese Kokai 1994-107900 describes the use of fatty acidester of polyvalent alcohol compound as an additive.

Problems that Invention Attempts to Solve

But, when a hydrazide compound is added as an additive to polyacetalresin, there is a certain danger of its byproduct, hydrazine itself,functioning as a reducing agent of photographic sensitive materials.Also, when a fatty acid ester of polyvalent alcohol compound is used asan additive, its effect to suppress formaldehyde is not sufficiently andpractical problems persist for its use as a resin composition to makemolded parts for photographic sensitive materials.

SUMMARY OF THE INVENTION

Resin compositions used to make parts for photographic sensitivematerials, which are polyacetal resin compositions and are characterizedby the concentration of formaldehyde generated from a formed object ofthe said composition in a closed environment being less than 20 ppm andby not compromizing with their photographic properties.

This invention is to solve the problems described above and aims atmaking polyacetal resins that possess excellent characteristics inmechanical properties, heat resistance and fatigue resistance suitableto be a resin composition material to make molded parts used forphotographic sensitive materials.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 is a schematic perspective view of an instant film pack used inthe invention.

FIG. 2 is a graph showing a correlation of formaldehyde concentrationand fogging concentration. Abscissa, left and right ordinates are forthe amounts of Additive-2 (weight %), the formaldehyde concentration(ppm) and the fogging concentration (Dmin), respectively. The top solidplot is for the fogging concentration at blue and the lower broke lineplot is for the residual formaldehyde concentration.

FIG. 3 is a graph showing a correlation between the amount of added5,5-dimethylhydantoin and the bending elasticity. The abscissa is theamount of Additive 2 (weight %) and the ordinate is the bendingelasticity (×10 kg/cm).

DETAILED DESCRIPTION

Method to Solve Problems

In order to achieve the above objective, this invention is to usepolyacetal resin, as a resin composition to make molded parts forphotographic sensitive materials, which is prepared in such a way thattheconcentration of formaldehyde formed from the molded parts remainbelow 20 ppm in a sealed vessel, without negatively affecting thephotographic quality. Concentration of formaldehyde gas generated frommolded parts made of this type of polyacetal resins is extremely smalland no chemical fogging due to reduction of silver halide emulsions canbe seen. Also, since it is designed not to produce harmful chemicalsthat may negatively affect the photography, it is ideally suited to beused as a resin composition used to make molded parts for photographicsensitive materials.

Furthermore, in cases that an antioxidant is to be added to the abovepolyacetal resin in order to prevent thermal deformation due tooxidation during heating, a hindered phenol type antioxidant may be usedin the range of 0.001˜1.0 weight % to effectively suppress thegeneration of formaldehyde gas. Whereas below 0.001 weight % littleeffect is observed, above 1.0 weight % not only photography isnegatively affected but physical properties also deteriorate. Also, theaddition of a light-shielding material in the range of 0.5˜25 weight %improves the shading ability necessary for the molded parts to be usedaround photographic sensitive materials, without compromising thechemical and physical properties of the polyacetal resin. Below 0.05weight %, light-shielding power cannot be secured and the objective toadd the additive cannot be met, but also it means an operating loss.Above 25 weight %, the physical strength deteriorates and the appearancealso suffers.

In FIG. 1, a film pack made of the polyacetal resin composition of thisinvention is briefly described. The pack main-body consists of abox-shapecasement 3 forming an exposure opening 2 and a bottom lid 5 towhich a plate spring 4 is attached. In the casement are stored alight-shielding sheet 6 and about 10 sheets of mono-sheet type instantfilm units 7. Whereas the polyacetal resin of this invention can be usedas the composition material for the casement 3, the plate spring 4, thebottom lid 5 and the light-shielding sheet 6, some appropriate parts ofthese maybe made of a polystyrene resin and other resins.

In addition to the exposure opening 2, the casement 3 has an exit slot 8and a notch 9 through which a raking claw inserts. As a bottom lid 5 isfastened to the bottom of the casement 3, a plate spring 4 pushes up theinstant film units 7 and shade sheet 6 stored in the pack main body sothat the shade sheet 6 covers the exposure opening 2 from the inside ofthe casement 3. Hereby, the instant film units 7 in the pack main bodycanbe kept from the light. Further, the exit slot 8 is covered byflexible shade film.

The instant film unit 7 is fitted with a developer pod 7 in which adeveloping solution is enclosed. A film pack is loaded into a camera andphotographing is ready once the shade sheet 6 is ejected. When a pictureis taken, a raking claw mounted in the camera insert itself through thenotch 9 to scrape out the instant film unit 7, that has been justexposed through the exposure opening 2, through the exit slot 8. Afterthis, developer rollers located inside the camera rotate as they squeezethe exposed instant film unit 7 coming out of the exit slot 8 and squashthe developer pod 7a as the film unit is ejected.

The plate spring 4 is to press the top unit of the instant film units 7stored in the pack main body against the internal side of the exposureopening 2 and to position the instant film unit 7 to be used for thenext photographing in the exposure position. Therefore, especially ifthe platespring is to be made of a resin, the resin must have sufficientelasticity as well as such characteristics that the elasticity is notlost after prolonged storage.

Resin compositions of this invention, even if used as a moldingcompositionto make the plate springs described above, have enoughelasticity as well as a characteristic that gives rise to little creepdeformation. Although resin compositions of this invention use apolyacetal resin as monomers, the polyacetal resins herein used arecommonly used polyacetal resins which are polymers or copolymers ofaldehydes, for example, formaldehyde and formaldehyde cyclic oligomerssuch as trioxane, tetraoxane etc., or polymers prepared bycopolymerization of these aldehydes with cyclic ethers or cyclicacetals, for example, ethylene oxide, propylene oxide, 1,3-dioxolaneetc.

The polyacetal resin has the main chain consisting of --(CH₂ O)_(n) --unit (n is a natural number) and/or --(CHR--O)_(n) -- unit (R is alkyl:n is a natural number) and is a linear polymer with end groups eitherunprotected or protected by groups such as --OCOCH₃, --OCH₃, --OCH₂ --OHand with the number averaged molecular weight of 10,000˜100,000,preferably 18,000˜70,000.

In order to lower the concentration of formaldehyde gas liberated frompolyacetal resins, it is preferred to add to 100 weight parts ofpolyacetal resin 0.05˜3.0 weight parts, preferably 0.06˜2.0 weight %,more preferably 0.067˜1.0 weight % of organic cyclic compound withactive imino group shown in a general formula (I). Here, R¹, R², R³ inthe general formula (I) represent divalent organic radicals formingthrough their covalent bondings a cyclic organic compound.

Chem. 1

General Formula (I) ##STR1##

It is desirable that the active imino compound has its imino grouphighly reactive so that, during and even after the polyacetal resin hascrystallized and solidified, it can still react with formaldehyde toform the methylol group as shown in the reaction formula (II).

Chem. 2

Reaction Formula (II)

    R--NH--R'+HCHO→R--N(CH.sub.2 OH)--R'(R--, R'-- represent monovalent organic radicals)

In order for the imino group to possess such reactivity, the electrondensity at the imino group must be sufficiently low sic to fulfill theconditions to induce nucleophilic reactions. Accordingly, organicradicalsdirectly linked to the imino group by a chemical bond must be ofelectron withdrawing. Such organic radicals, namely organic radicals R¹,R², R³ in the above formula (I), should preferably possess, at theposition linked to the imino group, --CO--, --COO--, --NH--, --NH₂,phenyl group, biphenyl group, naphthalene group etc.

Furthermore, if a chemical is to be added to polyacetal resin, it isessential that such a chemical does not separate out by melt mixing orthermally decompose. Thus, hydantoins and imidazole derivatives may begood examples of compounds represented by the formula (I). In thisinvention, hydantoin type compounds are preferred. Hydantoin compoundsmayinclude but not necessarily be limited to hydantoin,5,5-dimethylhydantoin,5,5-diphenylhydantoin and allantoin.

To the acetal resin composition used in this invention, one may add alubricant, a light-shielding material, an antioxidant, a heatstabilizer, appropriate plasticizers and fillers, if necessary, withinthe range not to negate the effects of this invention.

Representative lubricants that may be used for the acetal compositionsof this invention will be listed below together with their makers.

(1) Silicone Type Lubricants

Various grade dimethylpolysiloxanes and their modifications (Shin-etsuSilicone, Toray Silicone)

(2) Oleic Acid Amide Lubricants

Armoslip CP (Lion-Akzo), Neutron (Nihon Seika), Neutron E-18 (NihonSeika),Amide O (Nitto Chem.), AlfroF:10 (Nihon Yushi),DaiyamidC-200(Nihon Kasei) etc.

(3) Elka Acid Amide Type Lubricants

Alfro-F-10 (Nihon Yushi) etc.

(4) Stearic Acid Amide Type Lubricants

Alfro-S-10 (Nihon Yushi), Neutron2 (Nihon Seika), Diyamid200 (NihonKasei) etc.

(5) Bis-Fatty Acid Amide Type Lubricants

Bisamide (Nihon Kasei), Diyamide200Bis (Nihon Kasei), Armowax BBS(Lion-Akzo) etc.

(6) Non-ionic Surfactant Type Lubricants

Electro-Stripper-TS-2, Electro-Stripper-TS-8 (Kao Soap) etc.

(7) Hydrocarbon Type Lubricants

Liquid Paraffin, Natural Paraffin, Microwax, Synthetic Paraffin,Polyethylene Wax, Polypropylene Wax, Chlorohydrocarbons, Fluorocarbons

(8) Fatty Acid Type Lubricants

High Fatty Acids (Preferably higher than C sic), Oxy-Fatty Acid

(9) Ester Type Lubricants

Lower Alcohol Esters of Fatty Acids, Polyvalent Alcohol Esters of FattyAcids, Polyglycol Esters of Fatty Acids, Fatty Alcohol Esters of FattyAcids

(10) Alcohol Type Lubricants

Polyvalent Alcohols, Polyglycols, Polyglycerols

(11) Metal Soap

Compounds of higher fatty acids such as lauric acid, stearic acid,ricinolic acid, naphthenic acid, oleic acid, etc. with metals such asLi, Mg, Ca, Sr, Ba, Zn, Cd, Al, Sn, Pb, or another metal.

Also, as shading compounds to be added to secure the light-shieldingproperty the followings may be cited.

(1) Inorganic Compounds

A. Oxides: silica, diatomaceous earth, alumina, Titanium oxide, ironoxides, zinc oxide, magnesium oxide, antimony oxide, barium ferrite,strontium ferrite, beryllium oxide, pumice, pumice balloon, aluminafiber

B. Carbonate Salts: calcium carbonate, magnesium carbonate, dolomite

C. Silicate Salts: talc, clay, mica, asbestos, glass fiber, glassballoon, glass beads, calcium silicate, montmorillonite, bentonite, etc.

D. Carbon: carbon black, graphite, carbon fiber, carbon hollow balls,etc.

E. Others: iron powder, copper powder, lead powder, tin powder,stainless steel powder, pearl pigment, aluminum powder, molybdenumsulfide, boron fiber, silicon carbon fiber, brass fiber, potassiumtitanate, lead titanate zirconate, zinc borate, barium metaborate,calcium borate, sodiumborate, aluminum paste, talc. etc.

(2) Organic compounds

Wood meal (pine, oak, saw-dust, etc.), husk fiber (almond, peanuts,chaff, etc.), colored various fiber such as cotton, jute, paper piece,cellophanepiece, nylon fiber, propylene fiber, starch, aromaticpolyamide fiber, etc.

Among these shading materials, carbon black is preferred because thebleed-out amount can be reduced. The following classes of carbon blackareespecially preferred, gas black, furnace black, channel black,anthracene black, acetylene black, Ketchen carbon black, lamp black,lamp smoke, pinesmoke, animal black, vegetable black, etc.

In this invention, furnace carbon black is preferred for reasons ofshadingpower, the cost and improvement of physical properties, whereasas for shading material with the ability to prevent electric chargebuild-up acetylene carbon black and modified synthetic carbon black suchas Ketchencarbon black are preferred. Depending upon the requirement, itmay be desirable to mix the former with the latter to obtain desiredcharacteristics.

Whereas there are various modes to mix shading substance, a master batchmethod is preferred because of the cost, pollution invention, etc.Japanese Kokai 1965-26196 describes a method to prepare a master batchof polymer-carbon black by dispersing carbon black into a solution ofpolymerdissolved in organic solvent, and Japanese Kokai 1968-10362describes a method to prepare a master batch by dispersing carbon blackinto polyethylene.

To be used to make molded parts for photographic sensitive materials inthis invention, carbon black of pH 6.0˜9.0 with average powder diameterof 10˜120 μm is preferred because little fogging shows up onphotographic sensitive materials, because photosensitivity does notchange much and because lumps of carbon black as well as pinholes due tofish-eyes hardly appear even when it is added to the resin compositionof this invention. Among the carbon black, furnace carbon black havingespecially volatile components less than 2.0% and oil absorption greaterthan 50 ml/100 g is preferred. Channel carbon black, in addition tobeing expensive, often produces fogs on photographic sensitive materialsand, therefore, is not preferred. Even if it must be used for somereason, effects onto the photography should be investigated before it isselected.

The following carbon black on the market may be preferred; MitsubishiKaseiCarbon Black #20 (B), #30 (B), #33 (B), #40 (B), #44 (B), #45 (B),#50, #55, #100, #600, #2200 (B), #2400 (B), MA 8, MA 11, MA 100.

As imported products may be cited, for example, Cabot Co.'s Black Pearls2,46, 70, 71, 74, 80, 81, 607, etc., Regal 300, 330, 400, 660, 991,SRF-S, etc., Vulcan 3, 6, etc., Sterling 10, SO, V, S, FT-FF, MT-FF,etc. Furthercited may be Ashland Chemicals' United R, BB, 15, 102, 3001,3004, 3006, 3007, 3008, 3009, 3011, 3012, XC-3016, XC-3017, 3020; butnot limited to the ones listed above.

The amount of shading material to be added should be in the range of0.05˜25 weight %, preferably 0.1˜15 weight %, more preferably 0.5˜10weight %, and most preferably 1.0˜7.0 weigh %.

Also, it is desirable to add antioxidant to prevent thermaldeterioration of the resin and to suppress the formation of fish-eyesand lumps (non-homogeneous lump breakdown). Hindered phenol typeantioxidants are most preferred in this invention and are listed below.

1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene,tetrakismethylene-3-(3', 5'-di-tert-butyl-4'-hydroxyphenyl)propionatemethane, octadecyl-3,5-di-tert-butyl-4-hydroxy-hydrocinnamate,2,2',2'-tris(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxyethylisocyanurate,1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-di-methylbenzyl)isocyanurate,tetrakis(2,4-di-tert-butylphenyl) 4,4'-biphenylene diphosphite ester.

4,4'-Thio-bis(6-tert-butyl-O-cresol),2,2'-thio-bis(6-tert-butyl-4-methylphenol),tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane,2,2'-methylene-bis(4-methyl-6-tert-butyl-phenol),4,4'-methylene-bis(2,8-di-tert-butylphenol),4,4'-butylidene-bis(3-methyl-6-tert-butyl-phenol),2,6-di-tert-butyl-4-methylphenol,4-hydroxymethyl-2,6-di-tert-butylphenol,2,6-di-tert-butyl-4-n-butylphenol.

2,6-Bis(2-2'-hydroxy-3'-tert-butyl-5'-methylbenzyl)-4-methylphenol,4,4'-methylene-bis(6-tert-butyl-O-cresolsic,4,4'-butylidene-bis(6-tert-butyl-m-cresol),3,9-bis{1,2-dimethy-2b-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxyethyl}2,4,8,10-tetraoxaspiro5,5undecanemay be listed. Among these, those with melting point higher than 100°C., especially above 120° C., are preferred. As to the amount of thesehindered phenol type antioxidants to be added, 0.001˜1.0 weight % is therange, preferably 0.005˜0.8 weight %, more preferably 0.01˜0.5 weight%,and most preferably 0.02˜0.4 weight %.

Further, as for the heat stabilizer to be added to the resin compositionofthis invention there are polyamide compounds, especially nylonterpolymers,hydroxy containing polymers such as those described in U.S.Pat. No. 4,776,168 and 4,814,397, and nonmelting nitrogen or hydroxycontaining compounds described in Europe Patent Publication 0388809.More concretely,these are polyamide 6, polyamide 6/12 copolymer,polyamide 6/66/610 terpolymer, polyamide 6/66/612 terpolymer,ethylene-vinyl alcohol copolymer, acrylamide (co)polymer,acrylamide/N,N-methylenebis-acrylamide copolymer. In general, the totalamount of heat stabilizers to be added tothe polyacetal resincomposition is 0.5˜5.0 weight parts to 100 weight parts of acetal resin,preferably 0.05˜1.50 weight parts.

Molded parts of these polyacetal resin compositions may be formed by anymolding method including compressed molding, ejection molding, extrusionmolding, blow molding, rotary molding, melt spinning, and heat molding.Especially preferred for obtaining parts pertaining to this invention isejection molding.

EXAMPLES

Below, concrete examples of this invention are described together withcomparative examples, but this invention is not limited to thoseexamples mentioned here.

Polyacetal resins used in the following Practical Examples are DuPont'shigh flow grade polyacetal-homopolymers, Delrin® 900 PNC 10 (Trade Name:Melt Index 11.5 g/min) and Delrin® 1700 PNC 10 (Trade Name: MeltIndex18.0 g/min). The followings are prepared for additives to be addedtoprevent oxidation during resin heating and for the purpose of reducingevolution of formaldehyde gas.

Additive 1: Hydantoin (Mitsui Toatsu)

Additive 2: 5,5-dimethylhydantoin (Mitsui Toatsu)

Additive 3: Adipic acid hydrazide (Nihon Hydrazine Ind.)

Additive 4: Stearic acid monoglyceride (Riken Vitamin)

(1) Practical Example A

Delrin® 900 PNC 10 (5000 g) and Delrin 900 PNC 10 (5000 g) mixed with 25g of one of the above listed Additives 1˜4 are fed to a 35 mm biaxialscrew ejection molder to melt mix and cut to obtain 5 different kinds ofresins in the form of pellets. In this process, the resin temperaturewas 195°˜198° C. and the feed rate was about 30 kg/hr. Each resin pelletis molded using a 75 Ton Sumitomo NestalEjection Molder to obtain 5kinds of cylindrical test pieces A-1˜A-5.During the molding the resintemperature and mold temperature was 250° C. and 75° C., respectively.

The test pieces A-1˜A-5 thus prepared are placed and sealed, 5piecestogether (the total weight about 5 g), in a 1 L polyethylenecontainer and allowed to stand at room temperature for 24 hours.Concentration of formaldehyde in the container was measured usingFormalde Meter--MarklI (Lion Co. England) to the ppm level. Results areshown in Table 1.

                  TABLE 1    ______________________________________                            FORM-    HYDRA- HA-                   ADDED    ALDEHYDE ZIDE   LATION    TEST  AD-      AMOUNT   CONCEN-  EVAL-  EVAL-    PIECE DITIVE   (WT %)   TRATION  UATION UATION    ______________________________________    A-1   Additive 1                   0.06     15.8     ◯                                            ◯    A-2   Additive 2                   0.06     10.0     ◯                                            ◯    A-3   Additive 3                   0.06     13.4     Δ                                            Δ    A-4   Additive 4                   0.06     23.7     ◯                                            X-Δ    A-5   none     --       69.8     ◯                                            X    ______________________________________

As Table 1 shows, all the additives exhibited observable effects inreducing the formaldehyde concentration in the molded parts. Among them,the most effective was Additive-2. Observable but insufficient effectscanbe seen with a fatty acid type additive, Additive-4. With Additive-3,formaldehyde concentration can be suppressed to the level below 15 ppmbuthydrazine is slowly released, which reduces photographic sensitivematerials and negatively affects the quality of photography, in additionto being harmful to human body. Thus, the column of Hydrazide Ratingshowsthe degrees of effects that the hydrazide compound included inthose test pieces exerts. Also, on the basis of concentrations offormaldehyde, the extent of fogging on photographic sensitive materialsare shown in the column of Fogging Rating. The marks in these ratingcolumns indicate: Opencircle: good. Filled circle: practical possibleuses. Filled triangle: improvement required. X: not suitable forpractical uses.

(2) Practical Example B

To Delrin® 900 PNC 10 (9,800 g) is added 200 g of Additive-2, melt mixedthrough a 35 mm biaxial screw extrusion molder (Toshiba TEM 35) and cutto prepare Additive-2 concentrate in the form of pellets (a masterbatch). During this process, the resin temperature was 200° C. and thefeed rate was 25 kg/hr. The Additive-2 concentrate thus obtained iscalled Additive-A.

In the manner similar to that used in Practical Example (1), cylindricaltest pieces B-1˜B-7 were prepared using mixtures prepared from High FlowDelrin® D1700 PNC 10 pellets and Additive-A in different ratios. Here,Test Piece B-1 is a sample which does not contain Additive-A. Usingthese test pieces B-1˜B-7, formaldehyde concentrations weremeasuredunder the conditions identical with those used in PracticalExample A. Results are shown in Table 2.

                  TABLE 2    ______________________________________                            CONCEN-  HYDRA- HA-                  ADDITIVE  TRATION OF                                     ZIDE   LATION    TEST  D1700P  A         ADDITIVE 2                                     EVAL-  EVAL-    PIECE (WT %)  (WT %)    (WT %)   UATION UATION    ______________________________________    B-1   100.0   0.00      0.00     69.8   X    B-2   98.0    2.00      0.04     35.6   X-Δ    B-3   97.5    2.50      0.05     18.6   ⊕    B-4   97.0    3.00      0.06     10.0   ◯    B-5   96.7    3.33      0.067    4.2    ◯    B-6   95.0    5.00      0.10     4.6    ◯    B-7   90.0    10.00     0.20     4.3    ◯    ______________________________________

As Table 2 shows, it is clear that Additive-2 must be added more than0.05 weight % in order to reduce the formaldehyde concentration inmolded partsbelow such a level that no fogging shows up on photographicsensitive materials. However, if concentration of hydrazine inAdditive-2 becomes too high, it functions as a reducing agent tophotographic sensitive materials and becomes, also, harmful to humanbody. Thus, the amount of Additive-2 to be added should be maintained inthe range of 0.05˜3.0weight %, preferably 0.06˜2.0 weight % and mostpreferably 0.067˜1.0 weight %. Furthermore, since the elasticity ofmolded parts is considerably reduced if concentration of Additive-2exceeds 0.5 weight %, it may be problematic to use molded parts made ofthis resin as the material for springs.

(3) Practical Example C

Next, plate spring 4 shown in FIG. 1 was ejection molded using thecomposition identical with that used in Test Piece B-1˜B-6 in PracticalExample B. Various plate springs thus obtained were stored and sealedtogether with photographic sensitive materials in a dump-proof bag(humidity permeability: 0.5 g/m² /24 hr) at 50° C. for 3 days in a dryatmosphere. Here, FUJICOLOR NC-160 was used as photographic sensitivematerial.

Then, the photographic sensitive materials were removed and developed tomeasure the fogging concentration, Dmin, at blue color where fogging ismost pronounced. The fogging concentration Dmin represents theconcentration difference relative to the concentration on a standardphotographic sensitive material when the photographic sensitive materialalone is allowed to stand for 3 days under the conditions identical withthose described above. Table 3 summarizes the observed values and FIG. 2shows the correlation with formaldehyde concentration measured inPractical Example B.

                  TABLE 3    ______________________________________    ADDED AMOUNT                0.00   0.04   0.05 0.06 0.067                                             0.10 0.20    OF ADDITIVE 2    (WT %)    FORMALDEHYDE                69.8   25.6   18.6 10.0 5.00 4.60 4.20    CONCENTRATION    (ppm)    HALATION    1.5    1.2    1.0  0.99 0.97 0.93 0.85    DENSITY (D.sub.min)    ______________________________________

Graph in FIG. 2 shows that the concentration of chemical fogging causedby formaldehyde converges to the standard fogging concentration Dmin0.8±0.2 in blank tests as long as the amount of Additive-2, which hasthe ability to trap formaldehyde, exceeds 0.067 weight %. Since, withthisquantity range of the additive, the formaldehyde concentration canbe maintained below 5 ppm and the fogging concentration can also besuppressed below 1.0, there should be no problem to use this material inthe vicinity of photographic sensitive materials.

As described above, the effect of lowering formaldehyde concentrationsby increasing the amount of Additive-2 has been confirmed, but theelasticityof molded parts decreases if too much is added. FIG. 3 showsthe correlation between the amount of added Additive-2 and the bendingelasticity of molded parts. As the graph shows, the bending elasticitysignificantly diminishes if Additive-2 is added more than 0.5 weight %.Ifthe plate spring 4 shown in FIG. 1 is to be made of the polyacetalresin inthis invention, it is desirable to use Additive-2 in the rangelower than 0.5 weight %.

As shown above, if Additive-2 is added to the polyacetal resin to theextent of 0.05˜3.0 weight %, preferably 0.06˜2.0 weight %, theresidualformaldehyde concentration can be greatly reduced, and even if it isused together with photographic sensitive materials, there is nodangerthat fogging on the photographic sensitive material becomesproblematic. IfAdditive-2 is added in the range of 0.067˜1.0 weight %,the bending elasticity of molded parts hardly diminishes and no problemshould be encountered even if it is used to make springs.

The polyacetal resin of this invention with the characteristicsdescribed above can be used not only for magazines which storephotographic sensitive materials like the film packs mentioned earlier,but also as various types of parts such as those used in productionlines of photosensitive materials as well as sheet material, conveyerrollers and gears which may be used in cameras or near films andprinting paper.

Further, the followings may represent suitable practicable modes to beincluded in this invention.

(1) Resin compositions used for making molded parts for photographicsensitive materials described in claim 1, comprising polyacetal resinsandpolyacetal resin compositions containing at least an organic cycliccompound bearing an active imino group.

(2) Resin compositions used for making molded parts for photographicsensitive materials described in claim 1, comprising polyacetal resinsandpolyacetal resin compositions containing at least a hydantoincompound.

(3) Resin compositions used for making molded parts for photographicsensitive materials described in claims 1˜3 containing lubricant in0.01˜10 weight % or in one of the above mentioned practicable mode (1)or (2).

Effect of Invention

As explained above, since the polyacetal resin of this invention isprepared not to spoil photographic quality by maintaining concentrationofformaldehyde generated in a closed vessel below 20 ppm, no chemicalfoggingtakes place even if molded parts are used in the vicinity ofphotographic sensitive materials. In order to effectively reduce theconcentration of formaldehyde generated from polyacetal resins, hinderedphenol type compounds can be used as antioxidants to be added to thepolyacetal resin and, by adjusting the amount to the 0.001˜1.0 weight %range, fogging on photographic sensitive materials can be prevented.Further, suitable shading material may be added in the 0.5˜25 weight %range,therby chemical fogging can be avoided with certainty.

Furthermore, since molded parts made of the resins prepared above causeneither chemical nor optical fogging on photographic sensitivematerials, they can be used in various shapes such as magazines, sheetsand rollers. Since sufficiently elastic parts, also, can be easily made,they may be used as materials to prepare springs.

The object of the invention is to provide a resin composition thatreduces the concentration of formaldehyde generated from polyacetalresins and which does not bring about chemical fogging when it is usedas parts for photographic sensitive materials. Composition5,5-Dimethylhydantoin is added to polyacetal resin to trap formaldehydegenerated from the polyacetal resin, thereby reducing the generationconcentration of formaldehyde. The amount of 5,5-dimethylhydantoin to beadded is 0.05˜3.0 weight %, preferably 0.06˜2.0 weight %, and mostpreferably 0.067˜1.0 weight %.

We claim:
 1. A novel resin composition for use in applications requiringlow formaldehyde concentration levels, comprising:a) about 97 to about99.95 weight percent of a stabilized polyacetal polymer with capped endgroups; and b) about 0.05 to about 3 weight percent of an organic cycliccompound having an active imino group according to the formula: ##STR2##wherein R¹, R², and R³ represent divalent organic radicals and saidorganic cyclic compound is selected from the group consisting ofhydantoin derivatives and imidazole derivatives, andwherein a partmolded from said resin produces an atmospheric formaldehydeconcentration of less than about 20 ppm in an enclosed environment. 2.The resin composition of claim 1 wherein said stabilized polyacetalpolymer is capped by the group consisting of --OCOCH₃, --OCH₃, and--OCH₂ CH₂ OH.
 3. The resin composition of claim 1 wherein said organiccyclic compound is a hydantoin derivative selected from the groupconsisting of hydantoin, 5,5-dimethylhydantoin, 5,5-diphenylhydantoin,and allantoin.
 4. The resin composition according to claims 1, 2, or 3comprising about 0.05 to 3.0 weight percent of said organic cycliccompound.
 5. The resin composition according to claims 1, 2, or 3comprising about 0.06 to 2.0 weight percent of said organic cycliccompound.
 6. The resin composition according to claims 1, 2, or 3comprising about 0.067 to 1.0 weight percent of said organic cycliccompound.
 7. The resin composition according to claims 1, 2, or 3further comprising about 0.001 to 1.0 weight percent of a hinderedphenol-type antioxidant.
 8. The resin composition according to claims 1,2, or 3 further comprising about 0.05 to 25 weight percent of alight-shielding material.
 9. A molded part comprising the resincomposition according to claims 1, 2, or
 3. 10. The resin compositionaccording to claim 8 further comprising about 0.5 to 5.0 weight percentof a thermal stabilizer selected from the group consisting of: a) apolyamide; b) a non-melting nitrogen-containing polymer compound; and c)a hydroxyl-containing polymer compound.
 11. The resin compositionaccording to claim 8 further comprising a filler selected from the groupof: glass, fiber, carbon black or combinations thereof.
 12. A method forreducing formaldehyde concentration in a closed environment from amolded part comprising a polyacetal resin composition, said methodcomprising:a) blending about 97 to about 99.95 weight percent of astabilized polyacetal copolymer end-capped by --OCOCH3, --OCH3, or--OCH₂ CH₂ OH-- group with about 0.05 to about 3 weight percent of anorganic cyclic compound having an active imino group according to theformula: ##STR3## wherein R¹, R², and R³ represent divalent organicradicals and said organic cyclic compound is selected from the groupconsisting of hydantoin derivatives and imidazole derivatives, and b)shaping said blend into a molded part by injection molding, blowmolding, extrusion or coextrusion molding, compression molding, rotarymolding, melt spinning, heat molding, or vacuum forming,wherein a partmolded from said resin composition produces an atmoshpheric formaldehydeconcentration of less than about 20 ppm in an enclosed environment.